1. Field of the Invention
The present invention relates to a micrometer for measuring a dimension or the like of an object to be measured based on an axial displacement of a spindle.
2. Description of Related Art
A micrometer using a lead screw has been known as one of displacement measuring instruments.
The micrometer includes: a U-shaped frame; an anvil fixed to one end of the frame; a spindle that is screwed to the other end of the frame and is advanced and retracted relative to the anvil; an encoder that detects a displacement of the spindle; and a display that displays a measurement value obtained by processing a detection value detected by the encoder.
Among the micrometers, there has been known a micrometer including a constant pressure device for stabilizing a measurement force of the spindle (see, for instance, Patent Literature 1: JP-A-2011-220787).
The typical micrometer including the constant pressure device can measure by a substantially constant measurement force. However, practically, the measurement force varies to some extent.
Particularly, when an attitude of the micrometer at zeroset (where the spindle is brought into contact with the anvil and a display value is set at zero) is different from an attitude of the micrometer in measurement, for instance, when the attitude of the micrometer at zeroset is horizontal and the attitude of the micrometer in measurement is vertical, a weight of the spindle is added to the measurement force. Then, a deformation of the frame varies to cause a difference between a deformation of the frame at zeroset and a deformation of the frame in an actual measurement. Accordingly, repeatability of the micrometer is deteriorated to cause a measurement error.